Will a pacemaker interfere with plastic surgery of the breasts and arms?
Having a pacemaker does interfere with surgery where an electrocautery is used. One can use Bipolar electrocautery which does not interfere with the function of the pacemaker. However this is an issue that you need to discuss with your cardiologist and plastic surgeon before the surgery. The issue is why you needed the pacemaker and what other medical conditions and medication are you on?
In some cases the pacemaker can be stopped during surgery and restarted by the representative of the pacemaker manufacturer at the end of surgery. But this is a decision for the cardiologist.
A pacemaker doesn't preclude you from having cosmetic surgery but you should be discussing this with your surgeon and clearing it with your cardiologist. I am not sure what you mean by midline reconstruction but any scars between your breast will increase your risks for complications. Choose a reputable, board certified surgeon and he/she should be able to help you navigate the options that are available to you.